So-called electric vehicles that run on power charged to an in-vehicle battery are becoming popular in recent years. However, such electric vehicles have a difficulty that power becomes insufficient while the vehicle is running or the in-vehicle battery is damaged due to over-charging.
In order to solve this difficulty, as is disclosed, for example, in Patent Document 1, there is a technique of enabling a vehicle to wirelessly receive a supply of power from an outside source when power becomes insufficient and conversely enabling a vehicle to wirelessly supply power to an outside source when there is power to spare.
Also, for a system of this type, as is disclosed, for example, in Patent Document 2, there is a technique of making wireless power transmission and reception between vehicles feasible. Incidentally, in a case where wireless power transmission and reception is performed between vehicles, in particular, power cannot be transmitted and received efficiently unless running of each vehicle is controlled at a high degree of accuracy.    Patent Document 1: JP-A-2005-210843    Patent Document 2: JP-A-2005-168085